IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India,2002 
  
  
DATA FUSION BY HSV TRANSFORMATION AS MAIN TECHNIQUE 
FOR DETERMINATION OF Avicennia schaueriana Stapf & Leechman CANOPY GAPS 
IN ITACORUBI MANGROVE, BRAZIL 
Roque A. Sänchez Dalotto * 
* FICH - UNL, Water Sciences Faculty — Del Litoral Natl. University, 3000 Santa Fe, Argentina - 
sanlotto@hotmail.com 
Commission VII 
KEY WORDS: Mangrove, data fusion, canopy gaps, Avicennia schaueriana Stapf & Leechman, remote sensing 
ABSTRACT: 
Data fusion is an alternative for merging metric properties of aerial photographs and thematic richness of infrared digital surveyings. 
Layer-based stereo photointerpretation results are internally consistent, while design of layers is usually slow and sometimes 
subjective. Use of another spectral resolution is a way for classification image improvement, but not always same spatial resolution 
as photogrammetric systems is available. For determination of Avicennia schaueriana Stapf & Leechman canopy gaps using data 
fusion in Itacorubi mangrove, Brazil (27°34'S; 48°32'W), two remote sensing products were fused. As metric input, aerial 
photographs were scanned using a photogrammetric scanner. As thematic input, an aerial infrared surveying based on a 900nm 
digital reconnaissance system was carried out and 28 images were created. Images were georreferenced using digital cartography 
and later they were imported as raster layers into a geographic information system. Images were fused applying Kraus and Albertz 
data fusion techniques. Parallelepiped, minimum distance to means and maximum likelihood supervised classifications were used 
for canopy gaps quantification. Field-truth was obtained from a stereo photointerpretation. Optimal results for canopy gaps 
quantification were obtained using minimum distance to means supervised classification techniques based on data fusion of 
panchromatic colour aerial photographs and digital infrared surveyings. 
1. INTRODUCTION 
1.1 Environmental situation 
Canopy gaps are a distinctive feature in mangrove forest all 
around the world. Lightning creates most part of gaps during 
storms, but some authors observed that major canopy gaps are 
created by influence of low intertidal mudbanks and variations 
in water properties (SMITH, 1987; SMITH, 1992). There, 
mangrove trees and shrubs are exposed to more light than are 
individuals under the surrounding canopy. Soils temperature, 
photosynthetically active radiation, water physical and 
chemical properties and anoxia environment in gaps are 
different than mean mangrove conditions, so individuals cannot 
survive in this altered habitat, and progressively die creating the 
typical observed gap pattern with dead trees that remain 
standing for a long time. 
Experiences in mangrove gaps monitoring using multitemporal 
studies based on aerial photographs were made in Queensland, 
Australia. Percentages of mangroves trees in gap-phase were 
calculated (SMITH, 1992). 
Gaps are also present in Itacorubi mangrove (27°34'S; 
48°32'W), Brazil. As defined by its latitudinal localization, 
Itacorubi mangrove is an extra tropical formation. It is a relict 
area kept alive by a local deviation of Brazil stream, and one of 
the southernmost mangrove area located in America (IBGE, 
1990). Three species grow in this habitat: Avicennia 
schaueriana Stapf & Leechman, Laguncularia racemosa L. and 
Rhizophora mangle L. These species are usually found in 
Atlantic american mangroves (NEW MEXICO HIGHLANDS 
UNIVERSITY, 2001). The area is a typical basin mangrove as 
described by LUGO and SNEDAKER in WOODROFFE 
(1992), where Avicennia schaueriana Stapf & Leechman 
largely dominates over Laguncularia racemosa and Rhizophora 
mangle, covering 98.5% of the mangrove area (SANCHEZ 
DALOTTO, unpub. data). So most part of canopy gaps are 
restricted to areas with Avicennia schaueriana Stapf & 
Leechman trees. 
Itacorubi mangrove is located in the northeast border of 
Florianópolis city (pop.300.000). As the city grows, the 
mangrove supports a demographic impact, especially in terms 
of water pollution, garbage, buildings and roads construction. 
This critical situation is similar to other mangrove areas in the 
world (ROBERTSON & ALONGI, 1992; SMITHSONIAN 
MARINE STATION, 2001), so, environmental monitoring is 
needed. Pointing to minimize the problem, local legislation has 
defined the Itacorubi mangrove as a Permanent Preservation 
Area (SANTA CATARINA, 1969), but not always this legal 
situation has been respected (CAVALCANTI WALCACER, 
1993). Also, municipality legislation (FLORIANÓPOLIS, 
1998) protects the area, considering restrictions to constructions 
and land use. 
There are various remote sensing monitoring tools available for 
specific situations such as canopy gaps. In this way, Kraus and 
Albertz data fusion by hue-saturation-value transformation 
technique (KRAUS, 1990; ALBERTZ, 1991) is an alternative 
for merging metric properties of aerial photographs and 
thematic richness of infrared digital surveyings. 
As part of Itacorubi mangrove monitoring, a particular goal was 
to determinate and to compare areas of Avicennia schaueriana 
Stapf & Leechman canopy gaps obtained by application of 
   
   
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